If I start an iOS 9 debug session on a simulator (e.g. iPhone 6) from XCode 7, it needs minutes until I can see something, but not the running app, instead always the message "error: failed to attach to process ID ...". The splash screen occurs for a moment, but the app will not start. Sometimes if I wait 5 to ten minutes, it starts. This is also for small apps, like sample apps from WWDC. Is the problem my old iMac? It is a mid 2007 with 4GB RAM and a 2.4 GHz core 2 duo, Yosemite.
If I got it run, it runs faster after changes in source code. But I got only iPhone apps to run, not Apple Watch apps (possibly if I wait an hour?)